Investigations will be performed mainly on xenografts of human tumors growing in immunosuppressed mice, and will be designed to elucidate the response of tumors to combined treatment with radiotherapy and chemotherapy. The usefulness of xenografts will be evaluated, concentrating upon carcinoma of the pancreas and testicular tumors. Comparisons will be made with Lewis lung carcinoma and with the response seen in patients. Emphasis will be placed on the search for in vivo evidence of potentiation between cytotoxic drugs and radiation. The results will be correlated with tumor size, both at the start of treatment and during regression. Parallel studies will be made of normal tissue reactions in lung, bone marrow and intestine, and in a subsidiary investigation the action of electroaffinic radiosensitisers will be tested on the xenografts.